High output impedance current mirror with superior output voltage compliance

Abstract

A current mirror divides an input source voltage dynamically, to provide a controlled voltage that corresponds to an output load voltage. The correspondence between this controlled voltage and the output load voltage determines the correspondence between the output current and the input current. By dynamically adjusting the controlled voltage, the correspondence to the output load voltage can be maintained to very low voltage. Preferably, the output load voltage is also dynamically divided to provide a comparison voltage for comparing to the controlled voltage when the output load voltage is high, thereby providing the appropriate output current at high voltage levels. The combination of these two techniques provides a wide output voltage compliance, and a high output impedance.

I claim:  
     
       1. A current mirror that receives an input current, and provides an output current corresponding to the input current, comprising: 
       an input stage that is configured to receive the input current at an input voltage, and  
       an output stage that is configured to provide the output current at an output voltage,  
       wherein  
       the input stage includes:  
       a first voltage divider network that is configured to receive the input voltage and to provide therefrom a controlled voltage based on a first control signal, and  
       a first control device that is configured to receive a controlling voltage that is based on the output voltage, and to provide therefrom the first control signal to the first voltage divider network to control the controlled voltage to correspond to the controlling voltage, and wherein the first voltage divider network includes:  
       a first transistor;  
       a second transistor;  
       a third transistor; and  
       a fourth transistor;  
       wherein:  
       the first, second, third and fourth transistors each include a gate, a drain, and a source, and  
       the gate of the first transistor receives the first control signal,  
       the drain of the first transistor receives the input current at the input voltage,  
       the source of the first transistor is coupled to the drain of the second transistor,  
       the gate of the second transistor is coupled to the drain of the first transistor,  
       the source of the second transistor is coupled to a reference voltage, and  
       the controlled voltage is provided at the drain of the second transistor, and wherein:  
       the gate of the third transistor is coupled to the gate of the second transistor,  
       the source of the third transistor is coupled to the reference voltage, and  
       the drain of the third transistor provides the controlling voltage that is based on the output voltage, and  
       the first control device is configured to:  
       compare the controlled voltage at the drain of the second transistor with the controlling voltage at the drain of the third transistor, and  
       provide therefrom the first control signal at the gate of the first transistor, and wherein:  
       the drain of the fourth transistor providing the output current, and  
       the source of the fourth transistor being coupled to the drain of the third transistor; and  
       a second control device that is configured to control the gate of the fourth transistor, based on a comparison of the controlling voltage at the drain of the third transistor and the input voltage.  
     
     
       2. The current mirror of  claim 1 , wherein 
       the first voltage divider network includes a first transistor having a conductance that is determined by the first control signal, and  
       the controlled voltage is dependent upon the conductance of the first transistor.  
     
     
       3. The current mirror of  claim 2 , wherein 
       the first voltage divider network includes a second transistor that is in series with the first transistor, and  
       the controlled voltage appears at a node between the first transistor and the second transistor.  
     
     
       4. The current mirror of  claim 1 , wherein 
       the second control device is configured to control the gate of the fourth transistor, such that:  
       the fourth transistor acts as a closed switch when the controlling voltage at the drain of the third transistor is substantially less than the input voltage, and  
       the fourth transistor acts as a variable conductance device when the controlling voltage at the drain of the third transistor is substantially greater than the input voltage.  
     
     
       5. A current mirror that receives an input current, and provides an output current corresponding to the input current, comprising: 
       an input stage that is configured to receive the input current at an input voltage, and  
       an output stage that is configured to provide the output current at an output voltage,  
       wherein  
       the input stage includes:  
       a first voltage divider network that is configured to receive the input voltage and to provide therefrom a controlled voltage based on a first control signal, and  
       a first control device that is configured to receive a controlling voltage that is based on the output voltage, and to provide therefrom the first control signal to the first voltage divider network to control the controlled voltage to correspond to the controlling voltage, wherein  
       the output stage includes:  
       a second voltage divider network that is configured to receive the output voltage and to provide therefrom the controlling voltage, based on a second control signal, and  
       a second control device that is configured to receive the input voltage and the controlling voltage, and to provide therefrom the second control signal.  
     
     
       6. The current mirror of  claim 5 , wherein 
       the second control device is configured to compare the input voltage and the controlling voltage to provide the second control signal, and  
       if the controlling voltage is substantially less than the input voltage, controls the second voltage divider network such that the controlling voltage substantially equals the output voltage, and  
       if the controlling voltage is near to the input voltage, controls the second voltage divider network such that the controlling voltage differs from the output voltage based on a difference between the controlling voltage and the input voltage.  
     
     
       7. A method controlling an output current based on an input current, comprising: 
       determining a controlling voltage, based on an output voltage associated with the output current, and  
       controlling an input stage to provide a controlled voltage from an input voltage associated with the input current, based on the controlling voltage,  
       wherein  
       correspondence between the controlled voltage, and the controlling voltage provides correspondence between the output current and the input current, and wherein  
       controlling the input stage includes controlling conductance of a first device in a first series network that receives the input current, and  
       the controlled voltage corresponds to a voltage division of the input voltage, based on the conductance of the first device, and wherein controlling the conductance of the first device includes:  
       determining a difference between the controlled voltage and the controlling voltage, and  
       adjusting the conductance of the first device to reduce the difference, and wherein determining the controlling voltage includes:  
       controlling an output stage to provide the controlling voltage based on the controlling voltage and the input voltage.  
     
     
       8. The method of  claim 7 , wherein 
       controlling the output stage includes controlling conductance of a second device in a second series network that provides the output current, and  
       the controlling voltage corresponds to a voltage division of the output voltage, based on the conductance of the second device.  
     
     
       9. The method of  claim 8 , wherein 
       controlling the conductance of the second device includes:  
       comparing the controlling voltage and the input voltage, and  
       if the controlling voltage is much less than the input voltage,  
       setting the conductance of the second device to correspond to a closed switch,  
       else  
       setting the conductance of the second device inversely to a difference between the controlling voltage and the input voltage.  
     
     
       10. A method controlling an output current based on an input current, comprising: 
       determining a controlling voltage, based on an output voltage associated with the output current, and  
       controlling an input stage to provide a controlled voltage from an input voltage associated with the input current, based on the controlling voltage,  
       wherein  
       correspondence between the controlled voltage and the controlling voltage provides correspondence between the output current and the input current, wherein  
       determining the controlling voltage includes:  
       controlling an output stage to provide the controlling voltage based on the controlling voltage and the input voltage.  
     
     
       11. The method of  claim 10 , wherein 
       controlling the output stage includes:  
       comparing the controlling voltage and the input voltage, and  
       if the controlling voltage is much less than the input voltage,  
       setting the controlling voltage substantially equal to the output voltage,  
       else  
       setting the controlling voltage to substantially equal the input voltage.